This invention relates generally to electronic signal processing circuitry and in particular to an improved bipolar digitizer or analog to digital converter capable of accepting analog input signals of either polarity and providing quantized digital representations of such signals.
Numerous applications exist which require that analog signals be digitized for further processing and analysis by computers or the like. One instance of the need for such apparatus occurs in security alarm systems of the type which utilize a buried cable, such as a Miles cable, as the intrusion sensing device. Seismic stimuli resulting from the disturbance of the soil in the vicinity of the cable or magnetostrictive stimuli resulting from ferrous material brought into close proximity to the cable are each sufficient to generate electrical signals in the cable. With the aid of a digital signal processor, it becomes possible to characterize these signals with sufficient accuracy to discern certain unique digital signatures formed by human footsteps etc., intruding upon the security alarm system.
In seeking an analog to digital converter capable of adequately interfacing the Miles cable to a digital processor, it was found that commercially available devices of this type were deficient in one or more respects thus rendering them unsuitable for this application. Some, for example, were found to be incapable of processing bipolar signals. Others attained the required resolution at conversion rates much too low to support the aforementioned signal processing application. And still others could not handle a wide range of input voltage levels or were insensitive to low input voltage levels.